1. Field of the Invention
The present invention relates to a network connection device connecting different types of networks, and in particular to a data conversion control technique of performing conversion between data on a switched telephone network and packets on an IP (Internet Protocol) network.
2. Description of the Related Art
There has been a data communications network composed of a plurality of switched telephone networks connected by IP networks, which is called a VoIP (Voice over IP) network. In such a VoIP network, a VoIP gateway device is provided between a switched telephone network and an IP network to perform protocol conversion. More specifically, the VoIP gateway device converts an IP packet stream received from the IP network to a data stream to be transmitted to the switched telephone network, and vice versa.
Since a packet stream received from the IP network is composed of control packets and data packets, the VoIP gateway device converts the received data packets to, for example, a voice data stream while processing the control packets. Therefore, if the processor of the VoIP gateway device has a low signal-processing capability, then it is difficult to perform conversion from data packets to a voice data stream without a hitch, increasing the possibility of loss of packet and thereby reducing the quality of service such as the quality of reproduced voice. To avoid such a reduction in quality of service, it is necessary to provide the VoIP gateway device with a high-speed processor to increase in throughput.
However, the processing speed of a program-controlled processor is limited. When high-speed processing is needed to process voice and video packets, there is a high possibility that the conversion is not smoothly performed and thereby some packets are discarded.
There have been proposed several Internet telephony techniques in Japanese Patent Application Unexamined Publication Nos. 10-210080, 11-220549, and 11-275070. However, none of these publications teach any technique of increasing in throughput so as not to reduce in quality of service.